Radio frequency module

ABSTRACT

The module comprises at least: a first chip forming a heater element; a second chip forming a device whose operating characteristics vary with temperature change or whose maximum operating temperature is lower than the maximum operating temperature of the first chip; and a multilayer substrate which is comprised of a plurality of dielectric layers and a plurality of conductor layers and mechanically supports the first chip and the second chip with some of the conductor layers electrically connected with these chips. The module has at least one of the following means: means for conducting the heat generated by the first chip throughout the module; means for guiding the heat generated by the first chip from the module&#39;s top face side to its bottom face side; and means for interrupting heat conduction from the first conductor pattern on which the first chip is placed to the second conductor pattern on which the second chip is placed. Thereby, there is provided a compact radio frequency module with high integration in function.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to wireless communications andparticularly to radio frequency components for use in mobilecommunication terminals such as mobile phones and wireless communicationterminals such as wireless LAN, which feature increased function, highintegration, reduced size and low price.

[0003] 2. Description of the Related Art

[0004] With the growing tendency towards more compact wirelesscommunication terminals, there is demand for radio frequency componentsfor wireless communication terminals that fit into a smaller packagingarea. Conventionally, circuit of radio frequency parts have been dividedinto several blocks by function and the blocks have been manufacturedseparately as modules while efforts have been made to improvereliability, reduce size and increase integrtaion for each module. Forexample, methods of heat dissipation in power amplifier (hereinafterreferred to as PA) modules including power amplifiers as heater elementsare disclosed in JP-A No.27570/1997 and JP-A No. 147349/1995.

[0005] In recent years, JP-A No.8584/1997 and JP-A No. 266546/1999disclose techniques which produce more compact radio frequencycomponents with higher integration in function by combining moduleswhich would be separately manufactured in the former methods.

[0006] PA requires a heat dissipation structure because it consumes muchelectric power and generates heat. For this reason, various PA modulestructures for effective heat dissipation are disclosed: one example isa multilayer substrate which has, on its surface layer, an electricallyisolated metallized layer or a metallized layer connected to a groundinglayer (JP-A No.147349/1995) and another example concerns a structure ofa substrate in which the almost whole surface of the ceramic substrateis covered with a metal layer and through holes for heat dissipation areuniformly distributed almost all over the substrate (JP-A No.27570/1997).

[0007] However, these conventional techniques have the followingdrawback: in a module which integrates a power amplifier and a devicewhose operating characteristics vary with rise in temperature, namely adevice having sensitive temperature dependence of characteristics, on asubstrate, the influence of the heat generated by the PA on the devicehaving sensitive temperature dependence of characteristics is not takeninto consideration, or though it is taken into consideration to mount aPA and a deveice having sensitive temperature dependence ofcharacteristics together in a module, attention is not paid to the factthat part of the heat is conducted in the module substrate and then tothe above-said device having sensitive temperature dependence ofcharacteristics.

[0008] Therefore, in the conventional techniques, when a device havingsensitive temperature dependence of characteristics is mounted togetherwith a power amplifier on a substrate, the fair distance between boththe devices was needed to avoid the influence of the heat generated bythe power amplifier. Furthermore, a deterioration in electricalcharacteristics which is caused by change in characteristics withtemperature rise has been unavoidable. For this reason, it has beenimpossible to produce a compact, high performance radio frequency modulein the form of both a power amplifier, which generates heat, and adevice having sensitive temperature dependence of characteristics aremounted together.

SUMMARY OF THE INVENTION

[0009] The present invention introduces a new concept of suppressingtemperature rise in the part of a substrate where the above-mentioneddevice having sensitive temperature dependence of characteristics isplaced for a radio frequency module where a power amplifier and thedevice having sensitive temperature dependence of characteristics areintegrated, thereby solving the above problem and realizing a compact,high-performance radio frequency module.

[0010] The present invention focuses the structure of a radio frequencymodule which solves the above problem and particularly the arrangementof conductor layers.

[0011] According to one aspect of the present invention, a radiofrequency module comprises at least: a first chip forming a heaterelement; a second chip forming a device whose operating characteristicsvary with temperature change or whose maximum operating temperature islower than the maximum operating temperature of the first chip; and amultilayer substrate which is comprised of a plurality of dielectriclayers and a plurality of conductor layers and mechanically supports thefirst chip and the second chip with some of the conductor layerselectrically connected with these chips, wherein the first chip islocated on a conductor layer provided on the top face of the multilayersubstrate or on a first conductor pattern made on a conductor layerinside a cavity made in the multilayer substrate; the second chip islocated on a conductor layer provided on the top face of the multilayersubstrate or on a second conductor pattern made on a conductor layerinside a cavity made in the multilayer substrate; and when themultilayer substrate is fixed on another substrate, it is fixed with itsbottom face in contact with the other substrate, and the module has atleast one of the following means: means for conducting the heatgenerated by the first chip throughout the module; means for guiding theheat generated by the first chip from the module's top face to itsbottom face; and means for interrupting heat conduction from the firstconductor pattern to the second conductor pattern.

[0012] According to another aspect of the invention, a radio frequencymodule comprises at least: a first chip forming a heater element; asecond chip forming a device whose operating characteristics vary withtemperature change or whose maximum operating temperature is lower thanthe maximum operating temperature of the first chip; and a multilayersubstrate which is comprised of a plurality of dielectric layers and aplurality of conductor layers and mechanically supports the first chipand the second chip with some of the conductor layers electricallyconnected with these chips, wherein the first chip is located on aconductor layer provided on the top face of the multilayer substrate oron a first conductor pattern made on a conductor layer inside a cavitymade in the multilayer substrate; the second chip is located on aconductor layer provided on the top face of the multilayer substrate oron a second conductor pattern made on a conductor layer inside a cavitymade in the multilayer substrate; and when the multilayer substrate isfixed on another substrate, it is fixed with its bottom face in contactwith the other substrate and the first conductor pattern and anotherconductor pattern electrically connected with the first conductorpattern are isolated from the second conductor pattern and anotherconductor pattern electrically connected with the second conductorpattern at the conductor layer in which the second conductor pattern isformed and conductor layers closer to the top face of the multilayersubstrate than the conductor layer in which the second conductor patternis formed.

[0013] According to a further aspect of the invention, the firstconductor pattern and another conductor pattern electrically connectedwith the first conductor pattern are isolated from the second conductorpattern and another conductor pattern electrically connected with thesecond conductor pattern at the conductor layer in which the secondconductor pattern is formed and conductor layers closer to the top faceof the multilayer substrate than the conductor layer in which the secondconductor pattern is formed and the former conductor patterns areconnected with the latter ones at least at one of the conductor layerslocated closer to the bottom face of the multilayer substrate than theconductor layer in which the second conductor pattern is formed.

[0014] According to a further aspect of the invention, a radio frequencymodule comprises a first chip; a second chip whose heat value per unittime may be smaller than that of the first chip; and a multilayersubstrate comprised of a plurality of conductor layers and a pluralityof dielectric layers, wherein the first chip and the second chip areelectrically connected with any of the conductor layers, and there are afirst structure for conducting the heat generated by the first chiphorizontally in the module and a second structure for conducting theheat vertically in the module.

[0015] A conductor layer may be used for the first structure. Theconductor layer can conduct the heat generated by the first chiphorizontally. When the conductor layer extends to the substrate's outeredge area, it realize easier heat conduction in a substrate. Oneapproach to controlling the heat conductivity of the conductor layer isto cut off patterns in the conductor layer. To this end, part of theconductor layer may be removed or a groove may be made.

[0016] The first chip, for example a power amplifier, does not alwaysgenerate heat but turns on and off periodically in some cases. Theprimary object of the invention is to prevent the second chip from beingaffected by the heat generated by the first chip which is operating.

[0017] According to a further aspect of the invention, as a method forpreventing heat conduction from the first chip to the second chip, aheat isolation zone which crosses the line connecting the first chip andthe second chip is specified on the main surface of the multilayersubstrate and the conductor layer area corresponding to the projectionfrom the heat isolation zone is removed or a groove is made in the areacorresponding to the projection from the heat isolation zone. Theconductor layer area corresponding to the projection from the heatisolation zone may be removed in all the conductor layers or in a singleconductor layer. Also, the whole area corresponding to the projection orpart of the area may be removed.

[0018] One example of the second structure is a via hole.

[0019] To put the first chip and the second chip at the differentconductor layer each other is effective to reduce the thermal effect tothe second chip, because the distance between the first chip and thesecond chip becomes longer than that in case of mounting them on thesame layer.

[0020] According to the present invention, even when a first devicewhich has a power amplifying function and a second device which hassensitive temperature dependence of characteristics such as a surfaceacoustic wave device (hereinafter referred to as a “SAW” device) areintegrated on a substrate, the temperature rise of the area in which thesecond device is placed can be suppressed and its thermal interferencewith the first device can be reduced so that it is possible to provide acompact radio frequency module with higher integration in function whichallows the first device and the second device to operate normally andstably.

[0021] The use of a radio frequency module according to the presentinvention enables to realize of a more compact wireless communicationterminal or if the size of a wireless communication terminal is fixed,it offers more space for new additional functions.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The invention will be more particularly described with referenceto the accompanying drawings, in which:

[0023]FIG. 1 is a sectional view showing a first embodiment of thepresent invention;

[0024]FIG. 2 is a sectional view showing a second embodiment of thepresent invention;

[0025]FIG. 3A is a top view showing a conductor pattern on a conductorlayer 5 a according to the second embodiment of the present inventionand FIG. 3B is a top view showing a conductor pattern on a conductorlayer 5 b according to the second embodiment of the present invention;

[0026]FIG. 4C is a top view showing a conductor pattern on a conductorlayer 5 c according to the second embodiment of the present inventionand FIG. 4D is a top view showing a conductor pattern on a conductorlayer 5 d according to the second embodiment of the present invention;

[0027]FIG. 5E is a top view showing a conductor pattern on a conductorlayer 5 e according to the second embodiment of the present inventionand FIG. 5F is a top view showing a conductor pattern on a conductorlayer 5 f according to the second embodiment of the present invention;

[0028]FIG. 6 is a sectional view showing a third embodiment of thepresent invention;

[0029]FIG. 7 is a sectional view showing a fourth embodiment of thepresent invention;

[0030]FIG. 8 is a sectional view showing a fifth embodiment of thepresent invention;

[0031]FIG. 9 is a top view showing a conductor layer pattern accordingto the fifth embodiment of the present invention;

[0032]FIG. 10 is a sectional view showing a sixth embodiment of thepresent invention;

[0033]FIG. 11 is a sectional view showing a variation of the sixthembodiment of the present invention;

[0034]FIG. 12 is a perspective view showing a seventh embodiment of thepresent invention;

[0035]FIG. 13 is a perspective view showing an eighth embodiment of thepresent invention;

[0036]FIG. 14 is a sectional view showing a ninth embodiment of thepresent invention;

[0037]FIG. 15 is a perspective view showing a tenth embodiment of thepresent invention;

[0038]FIG. 16 is a sectional view showing the tenth embodiment of thepresent invention; and

[0039]FIG. 17 is another sectional view showing the tenth embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] Next, preferred embodiments of the present invention will bedescribed in detail referring to the accompanying drawings. In thefigures which illustrate the embodiments, components which have the samefunctions are designated by the same reference numerals and componentswhich are once explained will not be explained again.

[0041]FIG. 1 is a sectional view showing a radio frequency moduleaccording to a first embodiment of the present invention. The firstembodiment is a radio frequency module in which a power amplifier 1 anda SAW device 2 ( ) are mounted on a ceramic multilayer substrate 3. TheSAW device 2 in this embodiment has a function as a transmitting filter.The multilayer substrate 3 is composed of six dielectric layers 4 a, 4b, 4 c, 4 d, 4 e, 4 f and seven conductor layers 5 a, 5 b, 5 c, 5 d, 5e, 5 f, 5 g. According to the first embodiment, the power amplifier 1 ismounted by silver paste or solder on a conductor pattern 10 formed onthe conductor layer 5 a. The SAW device 2 is mountd by silver paste orsolder on a conductor pattern 13 formed on the conductor layer 5 einside a cavity 6 made by partially removing the dielectric layers 4 ato 4 d. The conductor pattern on the surface of each device and therelevant conductor layer of the multilayer substrate are connected bybonding wires 7. The cavity, in which the SAW device 2 is located, ishermetically sealed by a cover 40. With a passive device 8 and the likeon the top face of the multilayer substrate, the substrate top iscovered by a lid 50.

[0042] In this embodiment, the multilayer substrate 3 has two areas: afirst area 100 and a second area 200. The first area 100 includes thepower amplifier 1, the passive device 8 for its operation, a wiringpattern 101 which connects them, and a conductor pattern 102 whichserves as the ground for the power amplifier 1; the second area 200includes the SAW device 2 and a passive device 80 for its operation, awiring pattern 201 which connects them and a conductor pattern 202 whichserves as the ground for the SAW device 2.

[0043] The heat generated by the power amplifier 1 is conductedpartially from the module surface and partially through the conductorpattern 10 holding the power amplifier 1, then through conductor layersand dielectric layers or via holes 11 down to the bottom face 12 of themodule while being cconducted horizontally and vertically. From thebottom face 12, the heat goes, for example, through a motherboard (notshown) on which the module is mounted, before being forced out of themodule (for example, dissipated into the air).

[0044] In the present invention, the SAW device 2, which has sensitivetemperature dependence of characteristics, and the power amplifier 2 areintegrated on the same multilayer substrate 3 so it is necessary tominimize temperature rise of the conductor pattern 13 holding the SAWdevice 2 in order to prevent or reduce the possibility of deteriorationin the SAW device 2.

[0045] For this purpose, preferably the module should have either of thefollowing structures or a combination of them: one structure is suchthat the heat is conducted throughout the module to reduce rise in theoverall temperature of the module; another structure is such that theheat can easily emanate from the conductor pattern 10 holding the poweramplifier 1 or from the conductor pattern 13 holding the SAW device; anda further structure is such that the heat from the power amplifier 1 ishardly transfered to the conductor pattern holding the SAW device 2.

[0046] In the first embodiment of the present invention, in order tofacilitate heat conduction inside the module, as many conductors aspossible are provided in each of the first area 100 and the second area200. In the first embodiment there is an area 300 where conductors arenot connected between the area 100 and the area 200 at the followingconductor layers; conductor layers between the conducter layer in whichthe conductor pattern 13 is formed and the conductor layer in which theconductor pattern 10 is formed, namely conductor layer 5 a, 5 b,5 c,5 dand 5 e. Therefore, as the heat conducted from the conductor pattern 10passes mainly through conductors or via holes 11 and enters the firstarea 100, the heat conductivity becomes low in the area 300 and the heatis hardly conducted into the second area 200. As a result, the amount ofheat which is conducted into the second area 200 decreases. Also in thesecond area 200, as many conductors as possible are provided in order toconduct the incoming heat throughout the second area 200. Therefore, theamount of heat which is conducted to the conductor pattern 13 holdingthe SAW device 2 decreases so that the temperature rise of the conductorpattern 13 can be suppressed, resulting in a reduction in thetemperature rise of the SAW device 2.

[0047] Consequently, even when the power amplifier 1 and SAW device 2are ingtegrated into one module, the SAW device 2 can operate withstability.

[0048] Next, a second embodiment of the present invention is describedreferring to FIG. 2. FIG. 2 is a sectional view showing a radiofrequency module according to the second embodiment. The structure ofthe second embodiment is the same as that of the first embodiment exceptthat the multilayer substrate 3 is composed of five dielectric layersand six conductor layers and a cavity in which the SAW device 2 islocated extends from the dielectric layer 4 b to the dielectric layer 4e.

[0049] In this embodiment, a conductor pattern electrically connectedwith the conductor pattern 10 holding the power amplifier 1 is connectedwith another conductor pattern electrically connected with the conductorpattern 13 holding the SAW device 2 at the conductor layers 5 e and 5 fwhich are located below the conductor pattern 13. Between the conductorlayers 5 a to 5 d, there is an area 300 in which the conductor pattern10 holding the power amplifier 1 and the other conductor patternelectrically connected with the conductor pattern 10 are not connectedwith the conductor pattern 13 holding the SAW device 2 and the otherconductor pattern electrically connected with the conductor pattern 13.

[0050]FIGS. 3A to 5F respectively show the respective conductor patternson the conductor layers 5 a to 5 f. The power amplifier 1 is mounted onthe conductor pattern 10 as shown in FIG. 3A and the heat generated bythe power amplifier 1 is conducted through conductor patterns (shown inFIG. 3A to FIG. 5F) horizontally or mainly through the via holes 11vertically. In this embodiment, the power amplifier is held by theconductor pattern 10 (as shown in FIG. 3A) while the SAW device 2 isheld by the conductor pattern 13 (as shown in FIG. 3B). The module isdesigned so that the conductor pattern 14 (FIG. 3B), conductor pattern15 (FIG. 4C) and conductor pattern 16 (FIG. 4D), which are electricallyconnected through the via holes 11 to the conductor pattern 10, are notconnected with the conductor pattern 31 (FIG. 4C) and conductor pattern32 (FIG. 4D) which are electrically connected through via holes 30 tothe conductor pattern 13 holding the SAW device, at the same layerlevel. On the other hand, as shown in FIGS. 5E and 5F, the conductorpattern electrically connected with the conductor pattern 10 and theconductor pattern electrically connected with the conductor pattern 13are connected with each other at the conductor layers 5 e and 5 f, by aconductor pattern 17 and a conductor pattern 18, respectively.

[0051] As a consequence, the heat generated by the power amplifier 1 ishardly conducted to the conductor layer 5 b holding the SAW device 2 andthe conductor layers located adjacent to it, 5 a, 5 c and 5 d, whichcurbs the temperature rise of the conductor pattern 13 and enables theSAW device 2 to operate with stability.

[0052] The wiring which carries signals from the power amplifier 1 tothe SAW device 2 crosses the boundary zone between the first area 100 tothe second area 200 through a wiring pattern 60 provided on theconductor layer 5 d as shown in FIG. 4D. The area of wiring whichcarries signals from the power amplifier 1 to the SAW device 2 issmaller than that of the conductor patterns 10 and 14 and thus theamount of heat which is conducted from the first area 100 to the secondarea 200 is smaller. Accordingly, the influence of the heat conductedthrough the wiring pattern 60 on the SAW device 2 is not considerable sothe wiring pattern 60 need not always be provided on the conductor layer5 d; instead it may be provided on a layer above or below the conductorlayer 5 d.

[0053] Therefore, even when the power amplifier 1 and SAW device 2 aremounted on the same multilayer substrate 3, the adoption of thestructure as defined by the present invention reduces the influence ofthe heat generated by the power amplifier 1 on the SAW device 2, so itis possible to provide a radio frequency module which allows the SAWdevice 2 to operate with stability even when both the devices aredensely integrated in the substrate.

[0054] Next, a third embodiment of the present invention is described,referring to FIG. 6. FIG. 6 is a sectional view showing the thirdembodiment. The structure of the radio frequency module in the thirdembodiment is the same as that in the second embodiment except that viaholes 70 are provided between the conductor pattern 10 holding the poweramplifier 1 and the conductor pattern 13 holding the SAW device 2, inaddition to the via holes 11 located beneath the power amplifier 1.These via holes 70 further encourage the heat to be conductedvertically, thereby decreasing the amount of heat to be conductedtowards the conductor pattern 13 holding the SAW device 2. As aconsequence, the influence of the heat generated by the power amplifier1 on the SAW device 2 is reduced so it is possible to provide a radiofrequency module which allows the SAW device 2 to operate with stabilityeven when both the devices are densely integrated in the substrate.

[0055] Next, a fourth embodiment of the present invention is described,referring to FIG. 7. FIG. 7 is a sectional view showing the fourthembodiment. The structure of the radio frequency module in the fourthembodiment is the same as that in the second embodiment except thatthere is a groove 80 between the conductor pattern 10 holding the poweramplifier 1 and the conductor pattern 13 holding the SAW device 2. Thegroove 80 decreases the amount of heat to be conducted horizontally. Asa consequence, the influence of the heat generated by the poweramplifier 1 on the SAW device 2 is reduced so it is possible to providea radio frequency module which allows the SAW device 2 to operate withstability even when both the devices are densely integrated in thesubstarate.

[0056] Next, a fifth embodiment of the present invention is described,referring to FIG. 8. FIG. 8 is a sectional view showing the fifthembodiment. The structure of the radio frequency module in the fifthembodiment is the same as that in the second embodiment except that aconductor pattern 17 electrically connected with the conductor pattern10 holding the power amplifier 1 is electrically connected with a metallid 40 for the cavity 6 in which the SAW device 2 is located. Thedifference between the conductor layer 5 e in the second embodiment andthat in the fifth embodiment is explained below referring to FIG. 5E andFIG. 9.

[0057]FIG. 9 illustrates the conductor pattern on the conductor layer 5e in the radio frequency module according to the fifth embodiment whileFIG. 5E illustrates the conductor pattern on the conductor layer 5 eaccording to the second embodiment. In the second embodiment, an area 41which is in contact with the metal lid 40 for the cavity 6 is notelectrically connected with the conductor pattern 17 surrounding it. Onthe other hand, in the fifth embodiment, as shown in FIG. 9, theconductor pattern 17 is in contact with the area 41 which is in contactwith the metal lid 40. As a result, since the heat from the poweramplifier 1 is conducted to the metal lid 40, the heat is easier todisperse inside the radio frequency module than in the second embodimentand thus the overall temperature of the module is decreased, which leadsto a decrease in the temperature of the area in which the SAW device 2is located. Accordingly, the module structure according to thisembodiment makes the temperature rise of the conductor pattern 13holding the SAW device smaller than the module structure according tothe second embodiment. As a consequence, the adoption of the same modulestructure as defined by this embodiment reduces the influence of theheat generated by the power amplifier 1 on the SAW device 2 so it ispossible to provide a radio frequency module which allows the SAW device2 to operate with stability even when both the devices are denselyintegrated in the substrate.

[0058] Next, a sixth embodiment of the present invention is described,referring to FIG. 10. FIG. 10 is a sectional view showing the sixthembodiment. The structure of the module in this embodiment is the sameas that in the first embodiment except that the conductor pattern in thefirst area 100 and that in the second area 200 are not connected witheach other at the conductor layers 5 f and 5 g. Thus, the conductorpatterns which serve as the grounds in the first area 100 and the secondarea 200 are not connected at any layer, so horizontal heat conductionis smaller than in the first embodiment. This means that, although themodule temperature in the first area 199 may rise a little, the amountof heat which is conducted from the power amplifier 1 to the conductorpattern 13 holding the SAW device 2 can be reduced. Consequently it ispossible to provide a radio frequency module which allows the SAW device2 to operate with stability.

[0059]FIG. 11 shows a variation of the embodiment shown in FIG. 10. Ascan be seen from FIG. 11, in a situation that the radio frequency moduleaccording to the sixth embodiment of the present invention is mounted ona motherboard 350, a conductor-free zone 352 which fits the conductorfree area between the first area 100 and the second area 200 of theradio frequency module is made in a conductor pattern 351 on themotherboard 350 so that the heat which is conducted from the first area100 through the conductor on the motherboard 350 to the second area 200can be reduced. Hence, it is possible to provide a radio frequencymodule which allows the SAW device 2 to operate with stability even whenthe power amplifier 1 and the SAW device 2 are densely integrated in thesubstrate.

[0060]FIG. 12 shows a seventh embodiment of the present invention.

[0061]FIG. 13 shows an eighth embodiment of the present invention.

[0062]FIGS. 12 and 13 only show the shape of the multilayer substrate 3and the positional relationship between the power amplifier 1 and theSAW device 2 where the conductor patterns of the radio frequency moduleare omitted. Here, the conductor patterns on the respective layers aremuch the same as those in the embodiments mentioned earlier. In theseembodiments, the power amplifier 1 is located on the top face of themultilayer substrate 3 and the SAW device 2 is located inside the cavity6 made through the bottom of the substrate 3. The multilayer substrate 3is mounted on the motherboard 350.

[0063] In these embodiments, top view of the substrate of the radiofrequency module is not rectangular but L-shaped or U-shaped and thepower amplifier 1 and the SAW device 2 are located in the peripheralarea of the module as illustrated in FIGS. 12 and 13. The modulestructures according to these embodiments make it possible to increasethe distance between the power amplifier 1 and the SAW device 2 andthereby reduce heat conduction, resulting in a decrease in thetemperature of the area in which the SAW device 2 is located. Part ofthe heat conducted to the motherboard 350 is conducted throughthemotherboard 350 by the conductor pattern 351. Therefore, asillustrated in FIG. 13, the conductor pattern 351 on the motherboard 350may have a conductor-free area 352 between the SAW device 2 and thepower amplifier 1.

[0064] Referring to FIG. 14, a ninth embodiment of the present inventionis explained next. The ninth embodiment is the same as the embodimentsmentioned so far except that the power amplifier 1 is located inside acavity 90 made in the multilayer substrate 3. Like the embodiment shownin FIG. 6, this embodiment has via holes 70 between the power amplifier1 and the SAW device 2 in addition to the via holes beneath the poweramplifier 1 in order to help the heat conduct towards the motherboard.

[0065] Referring to FIG. 15, a tenth embodiment of the present inventionis explained next. FIG. 15 shows a radio frequency module which combinesnot only the power amplifier 1 and the SAW device but also an RF-IC 400.In FIG. 15, the SAW device is located in a cavity (not shown). Thisembodiment has different areas with different functions: a first area100 which includes the power amplifier 1 and components of a matchingcircuit for the power amplifier; a second area 200 which includes filtercomponents such as a SAW device, switch, capacitance and inductor; and athird area 500 which includes an RF-IC 400 and components related toRF-IC operation.

[0066] In this case, although the conductors which serve as the groundsfor the respective areas may be connected not within the multilayersubstrate 3 but on the motherboard 350 as in the embodiment shown inFIG. 10, from the viewpoint of suppressing the module temperature risecaused by the heat generated by the power amplifier 1 it is desirable touse a structure that conducts the heat throughout the module byconnecting conductor patterns as far as possible while at the same timepreventing the heat from being conducted to the conductor pattern (notshown) holding the SAW device.

[0067]FIG. 16 is a sectional view taken along the dotted line A-B ofFIG. 15. In the embodiment shown in FIG. 16, at the conductor layerholding the SAW device 2 and the conductor layers located above it, theconductors which serve as the grounds for the first area 100 and thirdarea 500 are continuous with each other. In addition, via holes 71 and72 are provided under the RF-IC chip 400 and the SAW device respectivelyso that the heat conducted to the third area 500 and the second area 200is guided to the motherboard (not shown). As a consequence, thetemperature rise of the conductor pattern 13 holding the SAW device 2 issuppressed and thus it is possible to provide a radio frequency modulewhich enables the SAW device 2 to operate with stability.

[0068]FIG. 17 shows another example of a radio frequency modulestructure. Needless to say, the radio frequency module structure is notlimited to that shown in FIG. 16; it is acceptable to employ the radiofrequency structure as shown in FIG. 17 in which, while the conductorpatterns which serve as the grounds for the second area 200 and thethird area 500 are continuous with each other, the conductor patterns inthe first area 100 are not connected at the conductor layer on which theconductor pattern 13 where the SAW device 2 is mounted and the conductorlayers located above that layer.

[0069] This approach, in which the power amplifier and SAW device areintegrated in a module as described above, combined with a integrationof a switch and an RF-IC in the module, makes it easier to design radiofrequency curcuit parts, requires a smaller number of man-hours forassembling, provides more handling ease and thus enables production ofterminals at lower cost than the conventional method in which componentsare individually assembled into a terminal.

[0070] As discussed so far, the adoption of a module structure accordingto the present invention makes it possible to provide a more compactradio frequency module which assures more stable operation of a SAWdevice with no deterioration in the SAW device performance than existingradio frequency modules.

[0071] It is apparent that the present invention is not limited to acombination of a power amplifier and a SAW device and may be applied toa combination of another type of heater element and another type ofdevice having sensitive temperature dependence of characteristics.

[0072] Furthermore, the invention may be embodied in any forms otherthan the above-mentioned embodiments without departing from the spiritand scope of the invention.

What is claimed is:
 1. A radio frequency module comprising at least: afirst chip forming a heater element; a second chip forming a devicewhose operating characteristics vary with temperature change or whosemaximum operating temperature is lower than the maximum operatingtemperature of the first chip; and a multilayer substrate which iscomprised of a plurality of dielectric layers and a plurality ofconductor layers and mechanically supports the first chip and the secondchip with some of the conductor layers electrically connected with thesechips, wherein the first chip is located on a first conductor patternmade on a conductor layer provided on the top face of the multilayersubstrate or on a conductor layer inside a cavity made in the multilayersubstrate; the second chip is located on a second conductor pattern madeon a conductor layer provided on the top face of the multilayersubstrate or on a conductor layer inside a cavity made in the multilayersubstrate; and the module has at least one of the following means: meansfor conducting the heat generated by the first chip throughout themodule; means for guiding the heat generated by the first chip from themodule's top face side to its bottom face side; and means forinterrupting heat conduction from the first conductor pattern to thesecond conductor pattern.
 2. The radio frequency module as claimed inclaim 1, wherein, when the multilayer substrate is fixed on anothersubstrate, it is fixed with its bottom face in contact with the othersubstrate and the heat generated by the first chip is conductedthroughout the radio frequency module at least through the firstconductor pattern and another conductor pattern electrically connectedwith the first conductor pattern, and the second conductor pattern andanother conductor pattern electrically connected with the secondconductor pattern.
 3. The radio frequency module as claimed in claim 1,wherein, when the multilayer substrate is fixed on another substrate, itis fixed with its bottom face in contact with the other substrate andthe first conductor pattern and another conductor pattern electricallyconnected with the first conductor pattern are electrically isolatedfrom the second conductor pattern and another conductor patternelectrically connected with the second conductor pattern at least at oneof the multilayer substrate conductor layers in which these patterns areformed.
 4. The radio frequency module as claimed in claim 1, wherein,when the multilayer substrate is fixed on another substrate, it is fixedwith its bottom face in contact with the other substrate and there arevia holes which at least connect the first conductor pattern and thebottom face of the module and there are also via holes which connect thebottom face of the module and a part of at least one of the followingconductors;another conductor pattern electrically connected with thefirst conductor pattern, the second conductor pattern and anotherconductor pattern electrically connected with the second conductorpattern.
 5. The radio frequency module as claimed in claim 1, wherein,when the multilayer substrate is fixed on another substrate, it is fixedwith its bottom face in contact with the other substrate and the firstconductor pattern and another conductor pattern electrically connectedwith the first conductor pattern are isolated from the second conductorpattern and another conductor pattern electrically connected with thesecond conductor pattern at the conductor layer in which the secondconductor pattern is formed and conductor layers closer to the top faceof the multilayer substrate than the conductor layer in which the secondconductor pattern is formed.
 6. The radio frequency module as claimed inclaim 5, wherein the first conductor pattern and another conductorpattern electrically connected with the first conductor pattern areisolated from the second conductor pattern and another conductor patternelectrically connected with the second conductor pattern at theconductor layer in which the second conductor pattern is formed andconductor layers closer to the top face of the multilayer substrate thanthe conductor layer in which the second conductor pattern is formed andthe former conductor patterns are connected with the latter ones atleast at one of the conductor layers located closer to the bottom faceof the multilayer substrate than the conductor layer in which the secondconductor pattern is formed.
 7. A radio frequency module comprising atleast: a first chip forming a heater element on a first surface of asubstrate; a second chip forming, on the second surface of thesubstrate, a device whose operating characteristics vary withtemperature change or whose maximum operating temperature is lower thanthe maximum operating temperature of the first chip; and a multilayersubstrate which is comprised of a plurality of dielectric layers and aplurality of conductor layers and mechanically supports the first chipand the second chip with some of the conductor layers electricallyconnected with these chips, wherein, the first chip is located on afirst conductor pattern which serves as a grounding conductor for thefirst chip; the second chip is located on a second conductor patternwhich serves as a grounding conductor for the second chip; and when themultilayer substrate is fixed on another substrate, it is fixed with itsbottom face in contact with the other substrate and the first conductorpattern and another conductor pattern electrically connected with thefirst conductor pattern are isolated from the second conductor patternand another conductor pattern electrically connected with the secondconductor pattern at the conductor layer in which the second conductorpattern is formed and conductor layers closer to the top face of themultilayer substrate than the conductor layer in which the secondconductor pattern is formed.
 8. The radio frequency module as claimed inclaim 7, wherein the first conductor pattern and another conductorpattern electrically connected with the first conductor pattern areisolated from the second conductor pattern and another conductor patternelectrically connected with the second conductor pattern at theconductor layer in which the second conductor pattern is formed andconductor layers closer to the top face of the multilayer substrate thanthe conductor layer in which the second conductor pattern is formed andthe former conductor patterns are connected with the latter ones atleast at one of the conductor layers located closer to the bottom faceof the multilayer substrate than the conductor layer in which the secondconductor pattern is formed.
 9. A module comprising at least: a firstchip forming a heater element on a first surface of a substrate; asecond chip forming, on the second surface of the substrate, a devicewhose operating characteristics vary with temperature change or whosemaximum operating temperature is lower than the maximum operatingtemperature of the first chip; and a multilayer substrate which iscomprised of a plurality of dielectric layers and a plurality ofconductor layers and mechanically supports the first chip and the secondchip with some of the conductor layers electrically connected with thesechips, wherein, the multilayer substrate is comprised of a laminationincluding a first conductor layer to an n-th conductor layer (n is aninteger equal to or larger than 2) lying one upon another from themodule's top to its bottom with a dielectric layer between neighboringconductor layers; the first chip is located on a first conductor layerand the second chip is located on an m-th conductor layer (m is aninteger which is larger than 1 and smaller than n) in a cavity made inthe multilayer substrate; among conductor patterns electricallyconnected with the first chip and with a grounding terminal for themodule, conductor patterns formed on the first to m-th layers are notelectrically connected with conductor patterns electrically connectedwith the second chip and with the grounding terminal for the module atthe first to m-th layers respectively; and the former conductor patternsare electrically connected with the latter ones at least at one of the(m+1)-th to n-th layers.
 10. The radio frequency module as claimed inclaim 9, comprising at least: a first chip forming a heater element on afirst surface of a substrate; a second chip forming, on the secondsurface of the substrate, a device whose operating characteristics varywith temperature change or whose maximum operating temperature is lowerthan the maximum operating temperature of the first chip; and amultilayer substrate which is comprised of a plurality of dielectriclayers and a plurality of conductor layers and mechanically supports thefirst chip and the second chip with some of the conductor layerselectrically connected with these chips, wherein a conductor patternused for reception or transmission of signals between the first chip andthe second chip may be located on any conductor layer of the multilayersubstrate..
 11. The radio frequency module as claimed in claim 9,wherein the second chip is located in a cavity made in the directionfrom the module's bottom to its inside and the cavity is covered by ametal plate and the first conductor pattern is electrically connectedwith the metal plate.
 12. The radio frequency module as claimed in claim9, wherein, in addition to the first chip and second chip, there is athird chip comprising a device which is lower in heat value than thefirst chip; and a third conductor pattern which serves as a ground forthe third chip is connected either with the first conductor pattern oranother conductor pattern electrically connected with the firstconductor pattern at any conductor layer of the multilayer substrate, orwith the second conductor pattern and another conductor patternelectrically connected with the second conductor pattern at anyconductor layer of the multilayer substrate.
 13. The radio frequencymodule as claimed in claim 9, wherein the module is equivalent to amodule comprised of a rectangular parallelepiped first multilayersubstrate portion and a rectangular parallelepiped second multilayersubstrate portion which are joined at 90 degrees, taking the shape ofthe letter L and the first chip is located on a substrate portioncorresponding to the first multilayer substrate portion and the secondchip is located on a substrate portion corresponding to the secondmultilayer substrate portion, or the module is equivalent to a modulecomprised of a rectangular parallelepiped first multilayer substrateportion, a rectangular parallelepiped second multilayer substrateportion and a rectangular parallelepiped third multilayer substrateportion which are joined at 90 degrees in sequence, taking the shape ofthe letter U and the first chip is located on a substrate portioncorresponding to the first multilayer substrate portion and the secondchip is located on a substrate portion corresponding to the thirdmultilayer substrate portion.
 14. The radio frequency module as claimedin claim 9, wherein the other substrate on which the radio frequencymodule is to be mounted has at least one conductor-free zone between theother substrate's conductor area corresponding to the area beneath thefirst conductor pattern and its conductor area corresponding to the areabeneath the second conductor pattern, when the radio frequency module ismounted on the other substrate.
 15. A radio frequency module comprising:a first chip; a second chip whose heat value per unit time may besmaller than that of the first chip; and a multilayer substratecomprised of a plurality of conductor layers and a plurality ofintermediate layers, wherein the first chip and the second chip areelectrically connected with some of the conductor layers, and there area first structure for conducting the heat generated by the first chiphorizontally in the module and a second structure for conducting theheat vertically in the module.
 16. The radio frequency module as claimedin claim 15, wherein the conductor layers are used as the firststructure.
 17. The radio frequency module as claimed in claim 15,wherein a heat isolation zone which crosses the line connecting thefirst chip and the second chip is specified on a surface of themultilayer substrate and the area corresponding to the projection fromthe heat isolation zone is removed in at least one of the conductorlayers.
 18. The radio frequency module as claimed in claim 15, wherein aheat isolation zone which crosses the line connecting the first chip andthe second chip is specified on a surface of the multilayer substrateand a groove is made in the area corresponding to the projection fromthe heat isolation zone
 19. The radio frequency module as claimed inclaim 15, wherein a structure which pierces the plural first conductorlayers is used as the second structure.